By default the Menu tabs are aligned from left to right. When you have selected Arabic as the preferred language, then you need to customize Sun Java System Messenger Express to align the Menu tabs from right to left.
To align the User Interface from right to left you need to remove a line from the ar/i18n.js file.
Aligning the User Interface from Right to Left shows the line that needs to be removed from the ar/i18n.js file.
.... i18n['dir'] = 'ltr' ....